Method and device for controlling an internal combustion engine

ABSTRACT

The invention relates to a method for stopping an internal combustion engine, wherein an amount of air which is supplied via an air metering device of the internal combustion engine, in particular a throttle flap ( 100 ), is reduced after a stopping order has been detected. According to the invention, the amount of air which is supplied via the air metering device of the internal combustion engine is again increased when the detected speed (n) of the internal combustion engine falls below a predefinable speed threshold value (ns), wherein an intake cylinder (ZYL 2 ) to which the amount of air is supplied does not enter any working cycle after the amount of supplied air has been increased.

BACKGROUND OF THE INVENTION

Particularly in the case of vehicles with start/stop technology, i.e.when the engine is frequently switched off and on again during normaldriving operation, comfortable running down of the internal combustionengine and rapid restarting of the internal combustion engine is ofgreat importance.

JP-2008298031 A describes a method in which the throttle valve of theinternal combustion engine is closed during rundown in order to suppressvibration. By means of this measure, the air charge in the cylinders inthe internal combustion engine is reduced, thus reducing the roughnessof rundown since compression and decompression are minimized.

To restart the internal combustion engine, however, as much air aspossible is required in the cylinders in which ignition takes place forthe restart. There is therefore a conflict of aims between rapid enginestarting (which requires a large quantity of air in the cylinder) andcomfortable, i.e. low-vibration, engine rundown (which requires a smallamount of air in the cylinder). This conflict of aims is resolved bymeans of the present invention.

Devices which modify the stroke profile particularly of the inlet valvesof the internal combustion engine and thus adjust the air charge in thecylinders are common knowledge in the prior art. In particular, the factthat the stroke profile of the inlet valves can be configured as desiredwithin wide limits by means of electrohydraulic actuators is known.Internal combustion engines with such electrohydraulic valve adjustmentdo not require a throttle valve. It is likewise known that the strokeprofile, particularly of the inlet valves, can be varied by adjustingthe camshaft. Devices of this kind and the throttle valve, with whichthe air charge in the cylinders can be modified, are also referred tobelow as air metering devices.

SUMMARY OF THE INVENTION

If a quantity of air supplied to the internal combustion engine isreduced by means of an air metering device and only increased againshortly before the internal combustion engine comes to a halt, “engineshake”, i.e. the generation of discernible vibration, can be avoided.This is achieved by initially reducing the quantity of air supplied tothe internal combustion engine as the internal combustion engine runsdown and increasing it again if a detected speed of the internalcombustion engine has fallen below a speed threshold value.

An increased quantity of air is then supplied to an inlet cylinder whichis in an intake stroke immediately after or during the increase in thequantity of air supplied, and it then has an increased air charge. Ifthis inlet cylinder then goes into a compression stroke, the increasedair charge acts as a gas spring, which exerts a high restoring torque ona crankshaft via the inlet cylinder ZYL2. Conversely, the respective aircharge in the cylinders which go into a downward movement exerts atorque on the crankshaft acting in the direction of the forward rotationof the crankshaft. However, since these cylinders going into a downwardmovement have a small air charge, the overall torque acting on thecrankshaft is a restoring torque.

If the speed threshold value is suitably chosen, it is possible toensure that the inlet cylinder no longer goes into a power stroke afterthe increase in the quantity of air metered in. This has the advantagethat compression of the increased air charge is avoided, preventingunwanted vibration.

It is particularly advantageous if the speed threshold value is selectedin such a way that the inlet cylinder just fails to go into the powerstroke after the increase in the quantity of air metered in. If thespeed threshold value is selected in such a way and if the speed of theinternal combustion engine is higher than the speed threshold value whena request for restarting is detected, it is possible to implement amethod for particularly rapid restarting of the internal combustionengine.

In order to reliably select precisely the speed threshold value whichensures that the inlet cylinder just fails to go into the power strokeafter the increase in the quantity of air metered in, the inventionproposes an adaptation method. For this purpose, it is necessary todefine suitable criteria, according to which the speed threshold valueis reduced or increased.

Reducing the speed threshold value if the inlet cylinder still passesthrough a top dead center position after the increase in the quantity ofair metered in and before the internal combustion engine comes to a haltis a particularly simple way of ensuring that vibration due toimpermissible passage through a top dead center position at a high aircharge is suppressed during the subsequent operation of the internalcombustion engine.

Increasing the speed threshold value if the inlet cylinder no longergoes into a compression stroke after the increase in the amount of airmetered in is a particularly simple way of ensuring that the inletcylinder exhibits an oscillatory behavior when stopping during thesubsequent operation of the internal combustion engine.

Modifying the speed threshold value in accordance with a reverseoscillation angle is a particularly simple way of ensuring that theinlet cylinder exhibits a defined oscillatory behavior in the futureoperation of the internal combustion engine.

Increasing the speed threshold value if the reverse oscillation angle isless than a specifiable minimum reverse oscillation angle ensures thatthe inlet cylinder just fails to reach the top dead center position witha particularly high degree of reliability.

If the speed threshold value is increased to a specifiable initialthreshold value, the adaptation method according to the invention hasdefined entry points and is therefore particularly robust.

If the selected magnitude of the initial threshold value is such thatthe inlet cylinder reliably passes through the top dead center position,this ensures that the speed threshold value ns is always adaptedstarting from values that are too high, making the adaptation methodparticularly simple.

The dead center positions are the simplest points at which to monitorthe speed of the internal combustion engine. If the system determines,at one dead center position, that the speed has fallen below the speedthreshold, the inlet cylinder is just going into the inlet stroke. Ifthe quantity of air metered in by the air metering device is increasedwhile the outlet valve of the inlet cylinder is still open, an increasedquantity of air is pumped into an exhaust pipe from an intake pipe. Thisleads to disadvantageous noise generation. If, on the other hand, thequantity of air metered in by the air metering device is increased toolate during the inlet stroke of the inlet cylinder, there is a highpressure drop between the intake pipe and the cylinder. In this case,the inflow of air leads to considerable unwanted noise generation. Tominimize this noise generation, it is advantageous if the quantity ofair metered in by the air metering device is increased immediately afterthe end of valve overlap in the inlet cylinder, i.e. immediately afterthe closure of the outlet valve.

Since the internal combustion engine is halted, fuel injection isswitched off. For rapid restarting of the internal combustion engine,this is disadvantageous since the cylinders do not contain an ignitablemixture. Since, in the method according to the invention, air is passedinto the inlet cylinder from the intake pipe, it is possible to ensure,given appropriate injection before the end of the inlet stroke, thatthere is an ignitable fuel/air mixture in the inlet cylinder. Since theinlet cylinder comes to rest in the vicinity of a bottom dead centerposition or in the compression stroke, this is very advantageous for arapid restart since a starter has to carry out a rotation of thecrankshaft of just 180° before ignition can take place in the inletcylinder.

If the fuel is injected before or immediately after the inlet cylindergoes into the inlet stroke, this is particularly advantageous formixture formation. In the case of intake pipe injection, the amount offuel metered in can be particularly finely metered and, in the case ofdirect injection, early injection of fuel is advantageous for theturbulent mixing of air and fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are explained in greater detail below withreference to the attached drawings, in which:

FIG. 1 shows an illustration of a cylinder of an internal combustionengine,

FIG. 2 shows schematically the profile of a number of characteristicquantities of the internal combustion engine as the internal combustionengine is stopped,

FIG. 3 shows the sequence of the method according to the invention forstopping the internal combustion engine,

FIG. 4 shows a speed profile during the stopping and restarting of theinternal combustion engine,

FIG. 5 shows a detailed view of the speed profile during the stoppingand restarting of the internal combustion engine,

FIG. 6 shows the sequence of the method according to the inventionduring the restarting of the internal combustion engine,

FIG. 7 shows schematically a final oscillatory motion of the internalcombustion engine at different speed threshold values, and

FIG. 8 shows the sequence of the method according to the invention fordetermining the speed threshold value.

DETAILED DESCRIPTION

FIG. 1 shows a cylinder 10 of an internal combustion engine having acombustion chamber 20, a piston 30, which is connected by a connectingrod 40 to a crankshaft 50. The piston 30 performs an up and down motionin a known manner. The reversal points of the motion are referred to asdead center positions. The transition from an upward motion to adownward motion is referred to as the top dead center position, whilethe transition from a downward motion to an upward motion is referred toas the bottom dead center position. An angular position of thecrankshaft 50, referred to as a crank angle, is conventionally definedrelative to the top dead center position. A crankshaft sensor 220detects the angular position of the crankshaft 50.

Air to be combusted is sucked into the combustion chamber 20 via anintake pipe 80 in a known manner during a downward motion of the piston30. This is referred to as the intake stroke or inlet stroke. Thecombusted air is forced out of the combustion chamber 20 via an exhaustpipe 90 during an upward motion of the piston 30. This is usuallyreferred to as the exhaust stroke. The quantity of air sucked in via theintake pipe 80 is set by means of an air metering device, in theillustrative embodiment a throttle valve 100, the position of which isdetermined by a control device 70.

Via an intake pipe injection valve 150, which is arranged in the intakepipe 80, fuel is injected into the air sucked out of the intake pipe 80,and a fuel/air mixture is produced in the combustion chamber 20. Thequantity of fuel injected through the intake pipe injection valve 150 isdetermined by the control device 70, generally by means of the durationand/or level of an activation signal. A spark plug 120 ignites thefuel/air mixture.

An inlet valve 160 at the inlet from the intake pipe 80 to thecombustion chamber 20 is driven via cams 180 by a camshaft 190. Anoutlet valve 170 at the inlet from the exhaust pipe 90 to the combustionchamber 20 is likewise driven via cams 182 by the camshaft 190. Thecamshaft 190 is coupled to the crankshaft 50. The camshaft 190 generallyperforms one revolution for every two revolutions of the crankshaft 50.The camshaft 190 is designed in such a way that the outlet valve 170opens in the exhaust stroke and closes in the vicinity of the top deadcenter position. The inlet valve 160 opens in the vicinity of the topdead center position and closes in the inlet stroke. A phase in whichthe outlet valve 170 and the inlet valve in one system are openedsimultaneously is referred to as valve overlap. Such valve overlap isused for internal exhaust gas recirculation, for example. The camshaft190 can be designed, in particular, for activation by the control device70, making it possible to set different stroke profiles for the inletvalve 160 and the outlet valve 170 in accordance with the operatingparameters of the internal combustion engine. However, it is alsopossible for the inlet valve 160 and the outlet valve 170 not to bemoved up and down by means of the camshaft 190 but by means ofelectrohydraulic valve actuators. In this case, the camshaft 190 and thecams 180 and 182 can be omitted. There is likewise no need for thethrottle valve 100 with such electrohydraulic valve actuators.

A starter 200 can be connected mechanically to the crankshaft 50 by amechanical coupling 210. The production of the mechanical connectionbetween the starter 200 and the crankshaft 50 is also referred to asmeshing. Release of the mechanical connection between the starter 200and the crankshaft 50 is also referred to as disengagement. Meshing ispossible only if the speed of the internal combustion engine is below aspeed threshold value dependent on the internal combustion engine andthe starter.

FIG. 2 shows the behavior of the internal combustion engine as theinternal combustion engine is stopped. FIG. 2 a shows the sequence ofthe various strokes of a first cylinder ZYL1 and of a second cylinderZYL2, plotted against the angle of the crankshaft KW. A first deadcenter position T1, a second dead center position T2, a third deadcenter position T3, a fourth dead center position T4 and a fifth deadcenter position T5 of the internal combustion engine are plotted.Between these dead center positions, the first cylinder ZYL1 runsthrough the exhaust stroke, the inlet stroke, a compression stroke and apower stroke in a known manner. In the illustrative embodiment of aninternal combustion engine having four cylinders, the strokes of thesecond cylinder ZYL2 are offset by 720°/4=180°. Based on the firstcylinder ZYL1, the first dead center position T1, the third dead centerposition T3 and the fifth dead center position T5 are bottom dead centerpositions, while the second dead center position T2 and the fourth deadcenter position T4 are top dead center positions. Based on the secondcylinder ZYL2, the first dead center position T1, the third dead centerposition T3 and the fifth dead center position T5 are top dead centerpositions, while the second dead center position T2 and the fourth deadcenter position T4 are bottom dead center positions.

FIG. 2 b shows the profile of a speed n of the internal combustionengine against time t in parallel with the strokes illustrated in FIG. 2a. The speed n is defined as the time derivative of the crank angle KW,for example. The first dead center position T1 corresponds to a firsttime t1, the second dead center position T2 corresponds to a second timet2, the third dead center position T3 corresponds to a third time t3,and the fourth dead center position T4 corresponds to a fourth time t4.Between each two successive times, e.g. between the first time t1 andthe second time t2, the speed initially rises briefly, and then fallsmonotonically. The brief rise in speed is due to the compression of theair charge in the cylinders. A cylinder running through a top deadcenter position compresses the air charge therein to the maximum extent,and therefore compression energy is stored therein. Part of thiscompression energy is converted into rotational energy as the internalcombustion engine continues to rotate.

FIG. 2 c shows the time profile of an activation signal DK of thethrottle valve 100 in parallel with FIG. 2 a and FIG. 2 b. As is knownfrom the prior art, the throttle valve 100 is initially closed as theinternal combustion engine is stopped, this corresponding to a firstactivation signal DK1. If, as illustrated in FIG. 2 b, the speed n ofthe internal combustion engine falls below a speed threshold value ns,e.g. 300 rpm, then, according to the invention, the throttle valve 100is opened at an opening time tauf, corresponding to a second activationsignal DK2. Here, the opening time tauf is selected in such a way thatit occurs shortly after the third dead center position T3, which is thenext dead center position after the speed n of the internal combustionengine falls below the speed threshold value ns. At the third deadcenter position T3, the second cylinder ZYL2 goes into the inlet stroke.In what follows, therefore, it is also referred to as inlet cylinderZYL2. In the illustrative embodiment, the opening time tauf coincideswith the end of valve overlap in the inlet cylinder, i.e. with the timeat which the outlet valve 170 of the inlet cylinder ZYL2 closes. Basedon the top dead center position of the inlet cylinder ZYL2, the openingtime tauf corresponds to an opening crank angle KWauf. To determine thetime at which the speed n of the internal combustion engine has fallenbelow the speed threshold value ns, the speed n of the internalcombustion engine can either be monitored continuously. Since the risein the speed n of the internal combustion engine is small after the deadcenter positions, and the opening time tauf is supposed to be shortlyafter a dead center position, however, it is also possible to check ateach dead center position of the internal combustion engine whether thespeed n of the internal combustion engine has fallen below the speedthreshold ns. In the illustrative embodiment illustrated in FIG. 2 b,the fact that the speed n of the internal combustion engine has not yetfallen below the speed threshold ns is detected at the first time t1 andthe second time t2. At the third time t3, the system detects for thefirst time that the speed n of the internal combustion engine has fallenbelow the speed threshold ns, and the throttle valve 100 opens.

The opening of the throttle valve 100 then allows a large quantity ofair to flow into the inlet cylinder in the inlet stroke. If the inletcylinder ZYL2 goes into the compression stroke after the fourth time t4,the compression work to be performed on the air charge, which is greatlyincreased relative to the other cylinders, exceeds the compressionenergy released in the expanding cylinders, and the speed n of theinternal combustion engine falls rapidly until it falls to zero at areverse oscillation time tosc. The rotary motion of the crankshaft 50 isnow reversed, and the speed n of the internal combustion engine becomesnegative. The reverse oscillation time tosc corresponds to a reverseoscillation angle RPW of the crankshaft 50 which is indicated in FIG. 2a. At a stop time tstopp, the internal combustion engine comes to ahalt. It should be noted that the time axis is depicted in a nonlinearmanner. In accordance with the drop in the speed n of the internalcombustion engine, the time interval between the third time t3 and thefourth time t4 is longer than the time interval between the second timet2 and the third time t3, which in turn is longer than the time intervalbetween the first time t1 and the second time t2. The fifth dead centerposition T5 of the internal combustion engine is not reached. In thetime interval between the reverse oscillation time tosc and the stoptime tstopp, the crankshaft 50 performs an oscillatory motion, duringwhich the second cylinder ZYL2 oscillates in the compression stroke andthe inlet stroke thereof, while the first cylinder ZYL1 oscillates in acorresponding manner in the power stroke and the compression strokethereof.

FIG. 3 shows the sequence of the method, which corresponds to the methodillustrated in FIG. 2. With the internal combustion engine running, itis determined in a stop detection step 1000 that the intention is toswitch off the internal combustion engine. This is followed by step1010, in which injection and ignition are switched off. The internalcombustion engine is thus in the rundown mode. There then follows step1020, in which the throttle valve is closed. In the case of internalcombustion engines with camshaft adjustment, a switchover to a smallercam can take place in step 1020 as an alternative, thus reducing the aircharge in the cylinders. In the case of internal combustion engines withelectrohydraulic valve adjustment, the valves of the internal combustionengine can be closed in step 1020. There follows step 1030, in which thesystem checks whether the speed n of the internal combustion engine hasfallen below the speed threshold value ns. If this is the case, step1040 follows. If this is not the case, step 1030 is repeated until thespeed n of the internal combustion engine has fallen below the speedthreshold value ns. In step 1040, the throttle valve 100 is opened atopening time tauf. In the case of internal combustion engines withcamshaft adjustment, it is possible instead for a switch to be made to alarger cam in step 1040, for example, resulting in an increase in theair charge in the inlet cylinder ZYL2. In the case of internalcombustion engines with electrohydraulic valve adjustment, the inletvalve 160 of the inlet cylinder ZYL2 can be activated in such a way instep 1040 that it is open during the inlet stroke of the inlet cylinderZYL2, thus increasing the air charge in the inlet cylinder ZYL2. Therefollows step 1060. In the optional step 1060, fuel is injected via theintake pipe injection valve 150 into the intake pipe 80 of the internalcombustion engine. This injection of fuel is performed in such a waythat a fuel/air mixture is sucked into the inlet cylinder ZYL2 in theinlet stroke. In step 1100, the method according to the invention ends.As illustrated in FIG. 2 b, the internal combustion engine oscillatesinto a stationary position, in which the inlet cylinder ZYL2 comes torest in the inlet stroke or in the compression stroke. Injection of fuelin step 1060 is advantageous for rapid restarting of the internalcombustion engine when it is an internal combustion engine with intakepipe injection.

FIG. 4 shows the time profile of the speed n of the internal combustionengine when stopping and restarting. The speed n of the internalcombustion engine falls during a rundown phase T_Auslauf in the mannerillustrated in FIG. 2 b, and finally the sign changes when the rotarymotion of the internal combustion engine is reversed at the reverseoscillation time tosc illustrated in FIG. 2 b. This is illustrated inFIG. 4 as the end of the rundown phase T_Auslauf and the beginning of anoscillation phase T_Pendel. While the rundown phase T_Auslauf is stillongoing, the system determines at a starting request time tstart thatthe internal combustion engine is to be restarted because, for example,the system has detected that a driver has pressed a gas pedal. Adetermined start request of this kind before the stop time tstopp, isalso referred to as a “change of mind”. In the oscillation phaseT_Pendel, the profile of the speed n of the internal combustion engineundergoes a resulting variation until it falls to a constant zero at thestop time tstopp illustrated in FIG. 2 b and remains there. In FIG. 4,the stop time tstopp marks the end of the oscillation phase T_Pendel.

In the prior art method for starting the internal combustion engine, theoscillation phase T_Pendel is followed by detection of the fact that theinternal combustion engine is stationary, the starter 200 is meshed, andthe starter is activated. After an activation dead time T_tot of thestarter 200 of, for example, 50 ms, which is not illustrated in FIG. 4,the starter 200 begins a rotary motion at a time tSdT and thus impartsmotion to the crankshaft 50 once again. In the method according to theinvention, in contrast, a first meshing time tein1 and, if appropriate,a second meshing time tein2 is determined. The first meshing time tein1and the second meshing time tein2 are characterized in that the speed nof the internal combustion engine is sufficiently low for the starter200 to be meshed. The first meshing time tein1 and the second meshingtime tein2 are determined by the control device 70. If the time intervalbetween the starting request time tstart and the first meshing timetein1 is longer than the activation dead time T_tot, the starter 200 ismeshed and activated in such a way that it begins a rotary motion at thefirst meshing time tein1. If the first meshing time tein1 is too closein time to the starting request time tstart, the starter 200 is meshedand activated in such a way that it begins a rotary motion at the secondmeshing time tein2.

FIG. 5 illustrates in detail the selection of the first meshing timetein1 and the second meshing time tein2. As described, the speed n ofthe internal combustion engine falls rapidly to zero after the openingtime tauf, and the internal combustion engine begins a reverse motion atreverse oscillation time t_osc. The first meshing time tein1 isdetermined by means of characteristic maps or by means of models storedin the control device 70, for example, after the opening of the throttlevalve 100 and corresponds to the estimated reverse oscillation timetosc. It is, of course, also possible for different times at which thespeed n of the internal combustion engine passes through zero to bepredicted and selected as the first meshing time tein1 instead of thereverse oscillation time tosc.

In addition to the passage of the speed n of the internal combustionengine through zero, a second meshing time tein2 can be selected, fromwhich time onwards it is ensured that the speed n of the internalcombustion engine will no longer leave a speed range in which meshing ofthe starter 200 is possible. This speed range is given, for example, bya positive threshold nplus, e.g. 70 rpm, up to which the starter 200 canbe meshed during a forward rotation of the internal combustion engine,and by a negative threshold nminus, e.g. 30 rpm, up to which the starter200 can be meshed during a reverse rotation of the internal combustionengine. Using characteristic maps, for example, the control device 70calculates that the kinetic energy of the internal combustion engine hasfallen from the second meshing time tein2 to such an extent that thespeed range [nminus, nplus] will no longer be exceeded. At the secondmeshing time tein2 or at any time after the second meshing time tein2,the starter 200 can be meshed and made to perform a rotary motion.

FIG. 6 shows the sequence of the method according to the invention forrestarting the internal combustion engine. Step 2000 coincides with step1000 illustrated in FIG. 3. In this step, a request to stop the internalcombustion engine is determined. There follows step 2005. In step 2005,the throttle valve is closed, or other measures, e.g. adjustment of thecams 180, 182 or appropriate electrohydraulic activation of the valves160 and 170, are taken in order to reduce the air charge in thecylinders. There follows step 2010.

In step 2010, the system determines whether a start request for startingthe internal combustion engine is determined while the internalcombustion engine is still running down, i.e. during the rundown phaseT_Auslauf illustrated in FIG. 4. If this is the case, step 2020 follows.If this is not the case, step 2090 follows. In step 2020, the systemchecks whether the speed n of the internal combustion engine is abovethe speed threshold value ns (if appropriate by a minimum amount, e.g.10 revolutions per minute). These checks can take place continuously orin synchronism with the crankshaft, in particular at each dead centerposition of the internal combustion engine. If the speed n of theinternal combustion engine is above the speed threshold value ns, step2030 follows and otherwise step 2070 follows.

In step 2030, the throttle valve is opened, or other measures, e.g.adjustment of the cams 180, 182 or appropriate electrohydraulicactivation of the valves 160 and 170, are taken in order to increase theair charge in the cylinder which is the next to be in the inlet stroke.Via the intake pipe injection valve 50, fuel is injected into the intakepipe 80. There follows step 2040, in which the inlet cylinder ZYL2 isdetermined, i.e. the cylinder in which the air charge will be the nextto show a significant increase in the inlet stroke. The inlet cylinderZYL2 goes into the inlet stroke and sucks in the fuel/air mixture in theintake pipe 80. The inlet cylinder ZYL2 then makes a transition to thecompression stroke. The speed n is higher than the speed threshold valuens. The speed threshold value ns is selected in such a way that theinlet cylinder ZYL2 just fails to pass through a top dead centerposition. At the speed n of the internal combustion engine, it istherefore ensured that the inlet cylinder ZYL2 passes through a top deadcenter position once again and makes a transition to the power stroke.There follows step 2050. In step 2050, the fuel/air mixture in the inletcylinder ZYL2 is ignited, accelerating the rotation of the crankshaft50, and step 2060 follows. In step 2060, further measures are carriedout in order to bring about starting of the internal combustion engine,in particular a fuel/air mixture being ignited in a corresponding mannerin the other cylinders of the internal combustion engine. With thestarting of the internal combustion engine, the method according to theinvention ends.

In step 2070, fuel is injected into the intake pipe 80 via the intakepipe injection valve 150. There follows step 2100.

In step 2090, the system checks, in a manner corresponding to step 1030illustrated in FIG. 3, whether the speed n of the internal combustionengine has fallen below the speed threshold value ns. If this is not thecase, the program branches back to step 2010. If this is the case, step2100 follows.

Step 2100 corresponds to step 1040 in FIG. 3. The throttle valve isopened or some other air metering device, e.g. a camshaft adjustmentsystem or an electrohydraulic valve timing system, is activated in sucha way that the quantity of air supplied is increased. There follows step2110.

In step 2110, the system determines whether there is a request forstarting the internal combustion engine. If this is the case, step 2120follows. If this is not the case, step 2110 is repeated until there is arequest for starting the internal combustion engine. In step 2120, thesystem checks whether the internal combustion engine is stationary. Thiscorresponds to the time period illustrated in FIG. 4 following the endof the oscillation phase T_Phase. If this is the case, step 2060follows, in which conventional measures for starting the internalcombustion engine are carried out. As illustrated in FIG. 4, theinternal combustion engine is started at a time tSdT.

If the internal combustion engine is not stationary in step 2120, step2150 follows. In step 2150, the first meshing time tein1 is predicted.This prediction is performed by means of a characteristic map, forexample. Using the speed n which was determined during a previouspassage through the top dead center position of the inlet cylinder ZYL2(at the fourth time t4 in the illustrative embodiment), the kineticenergy of the internal combustion engine can be determined and, from thesecond position DK2 of the air metering device, the air charge in theinlet cylinder ZYL2 and hence the strength of the gas spring compressedby the inlet cylinder ZYL2 in the compression stroke can be estimated.From this, it is possible to estimate the reverse oscillation time tosc,which is predicted as the first meshing time tein1. There follows step2160, in which the system checks whether the time difference between thefirst meshing time tein1 and the present time is greater than theactivation dead time T_tot of the starter 200. If this is the case, step2170 follows. If this is not the case, step 2180 follows.

In step 2180, the second meshing time tein2 is determined. As explainedin FIG. 5, the second meshing time tein2 is selected in such way thatthe speed n of the internal combustion engine from the second meshingtime tein2 onwards remains in the speed interval between the negativethreshold nminus and the positive threshold nplus. In the following step2190, the starter 200 is meshed and starting is carried out from thesecond meshing time tein2. There follows step 2060, in which the furthermeasures for starting the internal combustion engine are carried out. Asan alternative, it is also possible, in step 2180, to determine ameshing interval, during which the speed n remains between the negativethreshold nminus and the positive threshold nplus. In this case, thestarter 200 is meshed and starting carried out in the meshing intervalin step 2190.

Instead of an intake pipe injection valve 150, it is also conceivablefor injection valves of the internal combustion engine to be arranged inthe combustion chamber, i.e. to be configured as a direct injectionvalve. In this case, injection of fuel into the intake pipe immediatelyafter the opening of the throttle valve can be omitted. The only factorof importance is that fuel should be injected in a suitable manner intothe inlet cylinder ZYL2 before it is ignited upon restarting.

FIG. 7 illustrates the selection of the speed threshold value ns. FIG. 7a illustrates the oscillatory behavior of the inlet cylinder ZYL2 whenthe speed threshold value ns is correctly selected. At the opening crankangle KWauf, the inlet cylinder ZYL2 is in forward motion, passesthrough the bottom dead center position UT corresponding to the fourthdead center position T4 and reverses its direction of rotation at thereverse oscillation angle RPW. The further oscillatory motion of theinlet cylinder ZYL2 up to the stationary condition is shown onlyindicatively in FIG. 7 a.

FIG. 7 b illustrates the oscillatory behavior of the inlet cylinder ZYL2if the speed threshold value ns selected is too high. A speed thresholdvalue ns which is too high means that the kinetic energy of the internalcombustion engine is too high when the throttle valve 100 is opened,i.e. at the opening crank angle KWauf. This leads to the inlet cylinderZYL2 passing through the bottom dead center position UT corresponding tothe fourth dead center position T4 and then also the top dead centerposition OT corresponding to the fifth dead center position T5. Thisleads to unwanted vibration in the drive train, and is felt to beuncomfortable by the driver.

FIG. 7 c illustrates the oscillatory behavior of the inlet cylinder ZYL2if the speed threshold value ns selected is too low. A speed thresholdvalue ns which is too low means that the kinetic energy of the internalcombustion engine is too low when the throttle valve 100 is opened, i.e.at the opening crank angle KWauf. The inlet cylinder ZYL2 passes throughthe bottom dead center position UT corresponding to the fourth deadcenter position, but has a relatively large reverse oscillation angleRPW. If, in step 3020, it is determined that the speed n of the internalcombustion engine is higher than the speed threshold value ns, it is nolonger safe to assume that the inlet cylinder ZYL2 will rotate beyondthe top dead center position OT and hence that it will be possible tostart the internal combustion engine quickly.

The selection of the speed threshold value ns is therefore of centralimportance for the functioning of the method according to the inventionbut, on the other hand, it is very difficult since it depends onvariables which change during the life of the internal combustionengine, e.g. the friction coefficient of the engine oil used.

FIG. 8 describes an adaptation method, by means of which an initiallyspecified speed threshold value ns can be adapted in order to compensatefor errors in the initialization or changes in the properties of theinternal combustion engine. In step 3000, it is determined that there isa stop request to the internal combustion engine, and measures forstarting the internal combustion engine are initiated. In step 3010, thesystem checks, in a manner corresponding to step 1030, whether the speedn of the internal combustion engine has fallen below the speed thresholdns. If this is the case, step 3020 follows, in which the throttle valveis opened in a manner corresponding to step 1040. There follows step3030, in which the system checks whether the inlet cylinder ZYL2 hasalready passed through the bottom dead center position UT. If this isnot the case, step 3040 follows. If it is the case, step 3060 follows.

Step 3040 takes account of the case where the speed threshold value nsselected is so low that the internal combustion engine comes to a halteven before the inlet cylinder ZYL2 passes through the bottom deadcenter position UT. For this purpose, the system checks in step 3040whether the internal combustion engine is stationary. If this is not thecase, the program branches back to step 3030. If the internal combustionengine is stationary, step 3050 follows. In step 3050, the speedthreshold value ns is increased. There follows step 3100, with which themethod ends.

In step 3060, the rotary motion of the internal combustion engine ismonitored. If the internal combustion engine turns the inlet cylinderZYL2 further beyond the top dead center position OT, step 3070 follows.If the top dead center position OT is not reached, step 3080 follows. Instep 3070, the behavior is as illustrated in FIG. 7 b, and the speedthreshold value ns is reduced. There follows step 3100, with which themethod ends.

In step 3080, the reverse oscillation angle RPW is determined by meansof the crankshaft sensor 220, for example. There follows step 3090. Instep 3090, the system checks whether the reverse oscillation angle RPWis smaller than a minimum reverse oscillation angle RPWS, which is 10°for example. If the reverse oscillation angle RPW is smaller than theminimum reverse oscillation angle RPWS, the correct behavior shown inFIG. 7 a is present, and step 3100 follows, with which the method ends.If the reverse oscillation angle RPW is larger than the minimum reverseoscillation angle RPWS, the behavior illustrated in FIG. 7 c is present,and step 3050 follows, in which the speed threshold value ns isincreased.

The increase in the speed threshold value ns in step 3050 can eithertake place incrementally or the speed threshold value ns is increased toan initial threshold value nsi, at which it is ensured that the internalcombustion engine exhibits the behavior illustrated in FIG. 7 b, i.e.that the speed threshold value ns selected is then initially too high.The initial threshold value nsi can be designed as an applicablethreshold value, for example. It is selected in such a way that, withinthe scope of the operating parameters that are possible during theoperation of the internal combustion engine, e.g. variations in theleakage of the air charge, differences in the engine oil or individualdifferences in the scatter of the frictional effect of the internalcombustion engine, the internal combustion engine exhibits the behaviorillustrated in FIG. 7 b, i.e. that the inlet cylinder ZYL2 goes into thepower stroke.

As an option, it is also possible for the adaptation of the speedthreshold value ns to be carried out when restarting of the internalcombustion engine has not taken place correctly: the speed thresholdvalue ns is increased if the system has decided in step 2020 that thedetermined speed n of the internal combustion engine is higher than thespeed threshold value ns and if, after steps 2030, 2040 and 2050 arecarried out, it is ascertained in step 2060 that the inlet cylinder ZYL2(ZYL2) has not gone into the power stroke.

1. A method for stopping an internal combustion engine, in which aquantity of air supplied to the internal combustion engine via an airmetering device is reduced after a stop request has been detected,characterized in that the quantity of air supplied to the internalcombustion engine via the air metering device is increased again if adetected speed (n) of the internal combustion engine falls below aspecifiable speed threshold value (ns), wherein an inlet cylinder(ZYL2), to which the quantity of air is supplied, no longer goes into apower stroke after the quantity of air supplied is increased.
 2. Themethod as claimed in claim 2, characterized in that the speed thresholdvalue (ns) is reduced if the inlet cylinder (ZYL2) goes into the powerstroke after the quantity of air metered in is increased and before theinternal combustion engine comes to a halt.
 3. The method as claimed inclaim 1, characterized in that the speed threshold value is increased ifthe inlet cylinder (ZYL2) no longer goes into a compression stroke afterthe quantity of air metered in is increased.
 4. The method as claimed inclaim 1, characterized in that the specifiable speed threshold value ismodified in accordance with a reverse oscillation angle (RPW).
 5. Themethod as claimed in claim 4, characterized in that the speed thresholdvalue is increased if the reverse oscillation angle (RPW) is greaterthan a specifiable minimum reverse oscillation angle (RPWS).
 6. Themethod as claimed in claim 5, characterized in that the specifiablespeed threshold value (ns) is increased to a specifiable initialthreshold value (nsi).
 7. The method as claimed in claim 7,characterized in that the selected magnitude of the initial thresholdvalue (nsi) is such that the inlet cylinder (ZYL2) passes through thetop dead center position.
 8. The method as claimed in claim 1,characterized in that the quantity of air metered in by the air meteringdevice is increased immediately after the closure of an outlet valve(160) of the inlet cylinder (ZYL2).
 9. The method as claimed in claim 1,characterized in that fuel is injected in such a way that an ignitablefuel/air mixture is present in the inlet cylinder (ZYL2) when it leavesthe inlet stroke.
 10. The method as claimed in claim 1, characterized inthat fuel is injected before the inlet cylinder (ZYL2) goes into theinlet stroke.
 11. A computer program, characterized in that it isprogrammed for use in a method as claimed in claim
 1. 12. An electricstorage medium for an open-loop and closed-loop control device for aninternal combustion engine, characterized in that a computer program foruse in a method as claimed in claim 1 is stored on said medium.
 13. Anopen-loop and closed-loop control device for an internal combustionengine, characterized in that it is programmed for use in a method asclaimed in claim
 1. 14. The method as claimed in claim 1, wherein theair metering device is a throttle valve (100).
 15. The method as claimedin claim 1, characterized in that fuel is injected immediately after theinlet cylinder (ZYL2) goes into the inlet stroke.
 16. An electricstorage medium for an open-loop control device for an internalcombustion engine, characterized in that a computer program for use in amethod as claimed in claim 1 is stored on said medium.
 17. An electricstorage medium for a closed-loop control device for an internalcombustion engine, characterized in that a computer program for use in amethod as claimed in claim 1 is stored on said medium.
 18. An open-loopcontrol device for an internal combustion engine, characterized in thatit is programmed for use in a method as claimed in claim
 1. 19. Aclosed-loop control device for an internal combustion engine,characterized in that it is programmed for use in a method as claimed inclaim 1.